Various types of noise filters for removing noise of a vehicle-mounted electric component have been developed. For example, an anti-fog hot wire and a radio antenna are often provided together on the same rear glass of a vehicle. In such a case, a noise filter is connected in series to a wiring for supplying power to the hot wire so as to prevent, e.g., AM radio from being adversely affected by noise superimposed on the wiring.
In view of an installation space and influences on vehicle performance, a vehicle-mounted noise filter is required to be small in size and light in weight. For example, Patent Document 1 discloses a noise filter capable of achieving a reduction in size and heat radiation. In Patent Document 1, a noise filter constituted by a π-type low-pass filter is taken as an example. This noise filter has a filter circuit that has a function of allowing a direct current to pass therethrough and that achieves the maximum noise suppression amount (insertion loss) in AM radio band (medium-wave to short-wave band).